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Postings from October 2012
Dear all, After reading Reini's blog post, I spent a commute on adding a compile flag (-DNO_TAINT_SUPPORT) that replaces virtually all taint-related operations with no-ops. It's in a branch on camel at smueller/no_taint and can't go to blead quite as-is. The upshot is that a the basic script that I had used for profiling function call overhead now runs somewhere around 10-20% faster. Just compiling normally, I saw on the order of 18%. With Nicholas' set of "let's try to avoid alignment issues"[1] flags, I still see 12%. It's a micro-benchmark, so don't assign too much meaning. Either way, it's *known* to shed instructions. I would NOT want this to be the default behaviour, but having this an option could be a boon to people like my employer, who run Perl on thousands of machines and capacity is as important as latency. (Thus the eternal "you spend more time waiting for IO" doesn't apply.) I would love some review of the changes to the effect of what you think needs doing in order to get this into blead. Just to reiterate: This would be an opt-in perl.o-compile-time option to disable taint support in the perl binary. This is what I think needs doing still: - PL_taint_warn would likely deserve the same treatment as PL_taint and PL_tainted. - Obviously, tests fail. We have tests for -t/-T So we'd need a way from Perl to check for whether or not we have taint support and skipping the tests. - Right now, I added a Perl warn() on startup when -t/-T are detected but the perl was not compiled support it. It might be argued that it should be silently ignored! Needs some thinking. You could argue that perl should just throw an exception on -T/-t without support for it. For the tests, it would be kind of convenient to be able to just silently ignore -t/-T and then skip running the tests. - Code quality concerns of my patch - it just needs review. - Configure support required. Merijn, Andy, could you help me with this? - Needs thinking: How does this tie in with CPAN XS modules that use PL_taint and friends? It's easy to backport the new macros via PPPort, but that doesn't magically change all code out there. Might be harmless, though, because whenever you're running under NO_TAINT_SUPPORT, any check of PL_taint/etc is going to come up false. Thus, the only CPAN code that SHOULD be adversely affected is code that changes taint state. Any more sophisticated commetns than Reini's "10% don't matter"? Best regards, Steffen [1] -g -O2 -falign-loops=8 -falign-jumps=8 -falign-functions=64 -falign-labels=8 -mpreferred-stack-boundary=8 -minline-all-stringopsThread Next